Braking systems for rotorcraft

ABSTRACT

In some embodiments, a rotorcraft includes a fuselage having a rotor hub assembly protruding therefrom that is rotatable relative thereto. A generator having an armature is mechanically coupled to the rotor hub assembly such that the armature is rotatable in response to rotation of the rotor hub assembly. A braking unit is in selective electrical communication with the generator. The braking unit is adapted to apply an electrical resistance to rotation of the armature, thereby reducing a rotational speed of the rotor hub assembly.

TECHNICAL FIELD OF THE DISCLOSURE

The present disclosure relates, in general, to braking systems for useon rotorcraft and, in particular, to braking systems utilizingelectrical and/or hydraulic resistance to absorb the kinetic energy of arotor hub assembly of a rotorcraft, thereby slowing or stopping therotation of the rotor hub assembly.

BACKGROUND

A rotorcraft, such as a helicopter, includes a rotating rotor hubassembly that includes two or more rotor blades to generate lift andpropulsion. While rotating, the rotor hub assembly has kinetic energy,which must be reduced during braking operations, such as when therotorcraft lands. Rotorcraft brakes should also dissipate energy at arate deemed acceptable by the pilot, but slow enough to preventrotorcraft damage. Rotorcraft may have entire rotor brake subsystemsdevoted to reducing the rotational speed of the rotor hub assembly. Forexample, rotorcraft currently utilize disc-and-caliper braking systems,in which fluid pressure from a master cylinder drives caliper pistonsonto brake pads, which clamp on a rotating disc, thereby producingfriction that slows the rotor hub assembly. These existing systems arenot unlike the disc brakes used on some automobiles.

Traditional braking systems, such as disc-and-caliper systems, however,have several drawbacks. First, disc-and-caliper systems add significantweight to the rotorcraft, increasing the amount of lift needed to flythe rotorcraft, thereby consuming more fuel and reducing rotorcraftendurance. Second, disc-and-caliper systems take up valuable space inthe rotorcraft. Third, because they constitute an entirely separatesubsystem, disc-and-caliper systems add complexity to the brakingfunctionality of the rotorcraft. For example, disc-and-caliper systemsmay require sensors that ensure the caliper has released pressure afterbraking to prevent the heat generated between the brake pads and discfrom causing a fire. Fourth, disc-and-caliper systems can be expensive,adding to the overall cost of the rotorcraft. Accordingly, a need hasarisen for improved rotorcraft braking systems that reduce rotorcraftweight and are able to utilize existing components of the rotorcraft toachieve the braking functionality. A need has also arisen for improvedrotorcraft braking systems that are smaller, safer, less expensive anddo not contribute to the complexity of the rotorcraft in a detrimentalway.

SUMMARY

In a first aspect, a braking system for a rotorcraft having a rotor hubassembly includes a generator having an armature mechanically coupled tothe rotor hub assembly such that the armature is rotatable in responseto rotation of the rotor hub assembly and a braking unit in selectiveelectrical communication with the generator. The braking unit is adaptedto apply an electrical resistance to rotation of the armature, therebyreducing a rotational speed of the rotor hub assembly.

In some embodiments, the braking unit may include a resistor such as avariable resistor. In certain embodiments, the braking unit may includea rechargeable battery or other electrical component. In someembodiments, the generator includes at least one magnet at leastpartially surrounding the armature, wherein the magnet is non-rotatingrelative to the armature.

In a second aspect, a rotorcraft includes a fuselage and a rotor hubassembly protruding from the fuselage, the rotor hub assembly rotatablerelative to the fuselage. A generator having an armature is mechanicallycoupled to the rotor hub assembly such that the armature is rotatable inresponse to rotation of the rotor hub assembly. A braking unit is inselective electrical communication with the generator. The braking unitis adapted to apply an electrical resistance to rotation of thearmature, thereby reducing a rotational speed of the rotor hub assembly.

In some embodiments, the rotorcraft may include a gearbox containing aplurality of gears, wherein the armature is mechanically coupled to therotor hub assembly via at least one of the gears. In certainembodiments, the rotorcraft may include an engine operable toselectively provide rotational input to the rotor hub assembly, whereinthe rotor hub assembly is operable to freely rotate in response tomechanical disengagement between the engine and the rotor hub assembly.In some embodiments, the braking unit may apply the electricalresistance in response to a braking signal input from a pilot of therotorcraft.

In a third aspect, a braking system for a rotorcraft having a rotor hubassembly includes a hydraulic pump having an input shaft mechanicallycoupled to the rotor hub assembly such that the input shaft is rotatablein response to rotation of the rotor hub assembly and a braking unit influid communication with the hydraulic pump. The braking unit is adaptedto selectively provide a hydraulic resistance to rotation of the inputshaft, thereby reducing a rotational speed of the rotor hub assembly.

In some embodiments, the braking unit may include an orifice operable toadjust the hydraulic resistance applied to the input shaft of thehydraulic pump. In such embodiments, the braking system may include afluid reservoir in fluid communication with the orifice. The orifice mayinclude a solenoid valve. In certain embodiments, the braking unit mayinclude a hydraulic-powered component. In some embodiments, the brakingunit may include a hydraulic accumulator that is adapted to store apressurized fluid usable to power a hydraulic-powered component of therotorcraft.

In a fourth aspect, a rotorcraft includes a fuselage and a rotor hubassembly protruding from the fuselage, the rotor hub assembly rotatablerelative to the fuselage. A hydraulic pump has an input shaftmechanically coupled to the rotor hub assembly such that the input shaftis rotatable in response to rotation of the rotor hub assembly. Abraking unit is in fluid communication with the hydraulic pump. Thebraking unit is adapted to selectively provide a hydraulic resistance torotation of the input shaft, thereby reducing a rotational speed of therotor hub assembly.

In some embodiments, the rotorcraft may include a gearbox containing aplurality of gears, wherein the hydraulic pump is mechanically coupledto the rotor hub assembly via at least one of the plurality of gears. Incertain embodiments, the rotorcraft may include an engine operable toselectively provide rotational input to the rotor hub assembly, whereinthe rotor hub assembly is operable to freely rotate in response tomechanical disengagement between the engine and the rotor hub assembly.In some embodiments, the braking unit applies the hydraulic resistancein response to a braking signal input from a pilot of the rotorcraft.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the features and advantages of thepresent disclosure, reference is now made to the detailed descriptionalong with the accompanying schematic figures in which correspondingnumerals in the different figures refer to corresponding parts and inwhich:

FIGS. 1A-1B are schematic illustrations of an exemplary rotorcraftutilizing a braking system in accordance with embodiments of the presentdisclosure;

FIG. 2 is an isometric view of an electrical braking system for use on arotorcraft in accordance with embodiments of the present disclosure;

FIG. 3 is a side view of a generator for an electrical braking systemfor use on a rotorcraft in accordance with embodiments of the presentdisclosure;

FIG. 4 is a circuit diagram of an electrical braking system for use on arotorcraft in accordance with embodiments of the present disclosure;

FIGS. 5A-5C are various schematic side views of electrical brakingsystems having different braking units for use on a rotorcraft inaccordance with embodiments of the present disclosure;

FIG. 6 is an isometric view of a hydraulic braking system for use on arotorcraft in accordance with embodiments of the present disclosure; and

FIGS. 7A-7C are various schematic side views of hydraulic brakingsystems having different braking units for use on a rotorcraft inaccordance with embodiments of the present disclosure.

DETAILED DESCRIPTION

While the making and using of various embodiments of the presentdisclosure are discussed in detail below, it should be appreciated thatthe present disclosure provides many applicable inventive concepts,which can be embodied in a wide variety of specific contexts. Thespecific embodiments discussed herein are merely illustrative and do notdelimit the scope of the present disclosure. In the interest of clarity,all features of an actual implementation may not be described in thisspecification. It will of course be appreciated that in the developmentof any such actual embodiment, numerous implementation-specificdecisions must be made to achieve the developer's specific goals, suchas compliance with system-related and business-related constraints,which will vary from one implementation to another. Moreover, it will beappreciated that such a development effort might be complex andtime-consuming but would nevertheless be a routine undertaking for thoseof ordinary skill in the art having the benefit of this disclosure.

In the specification, reference may be made to the spatial relationshipsbetween various components and to the spatial orientation of variousaspects of components as the devices are depicted in the attacheddrawings. However, as will be recognized by those skilled in the artafter a complete reading of the present disclosure, the devices,members, apparatuses, and the like described herein may be positioned inany desired orientation. Thus, the use of terms such as “above,”“below,” “upper,” “lower” or other like terms to describe a spatialrelationship between various components or to describe the spatialorientation of aspects of such components should be understood todescribe a relative relationship between the components or a spatialorientation of aspects of such components, respectively, as the devicesdescribed herein may be oriented in any desired direction. Unlessotherwise indicated, as used herein, “or” does not require mutualexclusivity.

Referring to FIGS. 1A and 1B in the drawings, a rotorcraft isschematically illustrated and generally designated 10. Rotorcraft 10 hasa rotor hub assembly 12, which includes a plurality of rotor blades 14.The pitch of rotor blades 14 can be collectively and cyclicallymanipulated to selectively control direction, thrust and lift ofrotorcraft 10. Rotorcraft 10 has a landing gear system 16 to provideground support for rotorcraft 10. Rotor hub assembly 12 is supportedatop rotorcraft 10 by a mast 18, which connects rotor hub assembly 12 toa gearbox 20. The bottom end of mast 18 includes a main rotor gear 22that is located in gearbox 20. Gearbox 20 includes a plurality of gearsthat are mechanically coupled to an engine 24. As used herein, the term“coupled” may include direct or indirect coupling by any means,including moving and nonmoving mechanical connections. Engine 24provides mechanical and rotational energy to gearbox 20 via a driveshaft26. Rotor hub assembly 12 is rotatable in response to rotation outputfrom engine 24. Gearbox 20 also includes a transmission that is used toadjust the engine output from driveshaft 26 to a suitable rotationalspeed of main rotor gear 22 so that rotor hub assembly 12 rotates at adesired speed.

Rotor hub assembly 12 is rotatable relative to a fuselage 28 ofrotorcraft 10. In various operational circumstances, it may be necessaryto slow or stop rotor hub assembly 12 from rotating. After engine 24ceases to provide rotational input to rotor hub assembly 12, rotor hubassembly 12, due to inertia, continues to have kinetic energy in theform of continued rotation. Rotorcraft 10 includes a braking system 30that is operable to reduce, or halt, the rotational speed of rotor hubassembly 12. Braking system 30 may electrically or hydraulically resistthe continued rotation of rotor hub assembly 12 in response to a brakingsignal input from a pilot of rotorcraft 10 or elsewhere. Depending onthe embodiment, braking system 30 converts the kinetic energy of rotorhub assembly 12 into electrical energy, via a generator, or fluidpressure, via a hydraulic pump, which is then dissipated, stored and/orused to power other components of rotorcraft 10. In some embodiments,braking system 30 may utilize components that are already present onrotorcraft 10, such as an alternator or hydraulic pump, thereby reducingthe need for additional componentry. For example, braking system 30 mayutilize the hydraulic or electrical subsystems of rotorcraft 10 todynamically or regeneratively reduce the rotational speed of rotor hubassembly 12. Braking system 30 may also be used to apply differingbraking forces to rotor hub assembly 12 at different times, therebyreducing the potential for pilot error and allowing for modulatedbraking according to situational circumstances. Braking system 30 mayalso be used to prevent rotor hub assembly 12 from rotating at all, asmay be necessary in some operational circumstances, such as duringovernight storage.

Engine 24 selectively provides rotational input to rotor hub assembly 12by utilizing a clutch mechanism. Engine 24 may engage and disengage frommain rotor gear 22 and rotor hub assembly 12, via a clutch or one ormore gears, as necessary for the particular operation. For example, whenrotorcraft 10 is grounded, engine 24 may be disengaged from main rotorgear 22 such that rotational input from engine 24 is not transmitted tomain rotor gear 22. Also, when engine 24 does not provide rotationalinput to main rotor gear 22, such as when engine 24 is disengaged frommain rotor gear 22 or when engine 24 fails or slows, main rotor gear 22and rotor hub assembly 12 are permitted to freely rotate. In oneexample, a freewheeling unit may be interposed between main rotor gear22 and engine 24 to enable rotor hub assembly 12 to freely rotateregardless of the amount of rotational input engine 24 provides to mainrotor gear 22, if any. In this example, braking system 30 may be drivenfrom the rotor side of a freewheeling unit to absorb the kinetic energyof rotor hub assembly 12. When engine 24 ceases to provide rotationalenergy via drive shaft 26, the freewheeling unit allows rotor hubassembly 12 to freely rotate, thereby allowing braking system 30 toabsorb the kinetic energy of rotor hub assembly 12. Also, while brakingsystem 30 is shown to be located in gearbox 20, braking system 30 may belocated anywhere on rotorcraft 10.

While braking system 30 is shown to be operable with respect to rotorhub assembly 12, braking unit 30 may be operable to slow or stop anyrotor on rotorcraft 10, including tail rotor 32. Any number of brakingsystems 30 may be utilized on rotorcraft 10, including both electricaland hydraulic braking systems. Also, rotor hub assembly 12 and tailrotor 32 may each utilize one or more separate braking systems 30. Itshould be appreciated that rotorcraft 10 is merely illustrative of avariety of aircraft that can implement the embodiments disclosed herein.Indeed, braking system 30 may be utilized on any aircraft that hasrotating blades or turbines. Other aircraft implementations can includehybrid aircraft, tiltrotor aircraft, unmanned aircraft, gyrocopters anda variety of helicopter configurations, to name a few examples. Theillustrative embodiments may also be used on the propulsion systems ofairplanes, such as propellers or turbines. It should be appreciated thateven though aircraft are particularly well-suited to implement theembodiments of the present disclosure, non-aircraft vehicles anddevices, such as turbines, can implement the embodiments.

Referring to FIGS. 2 and 3 of the drawings, an electrical braking systemis schematically illustrated and generally designated 100. Electricalbraking system 100 is operable to slow or stop mast 102, which isconnected to the rotor hub assembly (not shown). In particular,electrical braking system 100 includes a generator 104 to which abraking force may be selectively applied by braking unit 106, therebyreducing the rotational speed of mast 102. Generator 104 includes anarmature 108 that is mechanically coupled to mast 102, and therefore therotor hub assembly, such that armature 108 is rotatable in response torotation of the rotor hub assembly. Armature 108 includes conductingwire capable of carrying current. In the illustrated embodiments,armature 108 includes coiled conducting wire. It will be appreciated byone of ordinary skill in the art that armature 108 may take many formsor shapes.

Generator 104 also includes one or more magnets 110 at least partiallysurrounding armature 108. Magnets 110 are non-rotating relative toarmature 108. Magnets 110 may be any type of magnet suitable for agenerator, such as permanent magnets or electromagnets. In someembodiments, generator 108 may be an alternator that is used to produceelectricity for the electrical components of the rotorcraft. Generator104 may be either an alternating current (AC) generator or directcurrent (DC) generator, depending on the application. Armature 108 ofgenerator 104 is mechanically coupled to mast 102, and therefore therotor hub assembly, via gears 112, 114, 116, 118. Gear 118 is a mainrotor gear, such as main rotor gear 22 in FIG. 1A. Armature 108 is alsomechanically coupled to mast 102 via shafts 120, 122. Mast 102, which isa shaft, protrudes from main rotor gear 118 to support the rotor hubassembly. Shaft 122 connects gear 114 to gear 116 and shaft 120 connectsgear 112 to armature 108. In the illustrated embodiment, generator 104is mounted on shaft 120. Via interconnected gears 112, 114, 116, 118,shafts 120, 122 and mast 102, armature 108 rotates in response torotation of the rotor hub assembly. Thus, the braking force provided bybraking unit 106, which provides an electrical resistance to therotation of armature 108, provides resistance to the rotation of shaft120, which in turn resists the rotation of the rotor hub assembly viagears 112, 114, 116, 118, shafts 120, 122 and mast 102.

The exact connection of armature 108 to the rotor hub assembly via gears112, 114, 116, 118, shafts 120, 122 and mast 102 is for purposes ofillustration only. Generator 104 may be located on any rotating portionof the drive system of the rotorcraft that is mechanically coupled tothe rotor hub assembly. Indeed, generator 104 may be mounted on mast 102itself. Any number of gears, shafts or other parts may be mechanicallycoupled between generator 104 and the rotor hub assembly, while stillallowing armature 108 to rotate in response to the rotation of the rotorhub assembly. In some embodiments, generator 104 may be on the rotorside of a freewheeling unit such that armature 108 rotates in responseto rotation of the rotor hub assembly even in the absence of rotationinput from an engine, such as engine 24 in FIG. 1A. In one example,shaft and gear 125 may be rotated, directly or indirectly, by theengine, which provides rotational energy to main rotor gear 118 viagears 114, 116. In this example, the engine may be engaged or disengagedfrom shaft and gear 125 by a clutch. A freewheeling unit may also becoupled to shaft and gear 125 so that insufficient input from the enginedoes not stall or prevent the free rotation of main rotor gear 118.

Braking unit 106 is in selective electrical communication with generator104. Armature 108 includes a commutator 126, which is rigidly coupled toand rotates with armature 108. Braking unit 106 is electrically coupledacross commutator 126. Braking unit 106 may be coupled to commutator 126via electrical-conducting wires 128, 130. Wires 128, 130 may beelectrically coupled to commutator 126 via electrical-conductingbrushes. Braking unit 106, when engaged, contributes an electrical loadto the illustrated circuit running through armature 108, which causeselectrical resistance to the rotation of armature 108 amidst magnets110, thereby reducing the rotation of the rotor hub assembly.

Braking unit 106 may be in selective electrical communication witharmature 108 via a switch 132. Switch 132 may be closed in response to abraking signal input from a pilot of the rotorcraft or elsewhere,thereby closing the electrical circuit between generator 104 and brakingunit 106 to cause armature 108 to reduce rotational speed. However, itwill be appreciated that braking unit 106 may be electrically coupled toarmature 108 in a variety of ways to cause the braking unit 106 to beselectively applied as an electrical load on the circuit. In applyingbraking unit 106, the kinetic energy of the rotor hub assembly isconverted into electrical energy by generator 104. Braking unit 106 maydissipate or store the generated energy, or may use the generatedelectrical energy in other parts of the rotorcraft.

In the embodiments in which generator 104 is an alternator that is usedfor other purposes on the rotorcraft, electrical braking system 100reduces the number of additional parts needed to stop or slow the rotorhub assembly, as existing componentry is utilized. Such re-use ofexisting componentry reduces rotorcraft weight, complexity and costs. Inother embodiments, generator 104 may also be used as a motor thatrotates the rotor hub assembly. In this embodiment, generator 104, whenused as a motor, may be powered by an external electrical power sourceto rotate armature 108 and therefore the rotor hub assembly. Forexample, an engine, such as engine 24 in FIG. 1A, may be used to powerthe motor, and this motor may be used as generator 104 when braking unit106 is applied thereto. When the motor changes its function to agenerator, the flow of the current and torque may reverse to cause rotorhub assembly to reduce its rotational speed. Also, multiple electricalbraking systems 100 may be utilized for the rotor hub assembly. Multipleelectrical braking systems 100 may allow the braking resistance to befine-tuned or sized appropriately to the particular rotorcraft.

Electrical braking system 100 may also allow an electrical braking inputto be used by a pilot, computer or other device to reduce the rotationof the rotor hub assembly. For example, braking functions may bemodulated electronically so as to prevent a pilot from over-applying thebrakes, as can happen in a disc-and-caliper braking system. An activebraking system may also allow the electrical resistance applied toarmature 108 to be varied over time, or depending on the operationalcircumstances. Also, allowing for braking to be initiated via electronicbraking input eliminates the need for a pilot of the rotorcraft to use amanual lever, as is used in a disc-and-caliper system. Such levers canbe heavy and difficult to use, especially during critical flightoperations.

Referring to FIGS. 4 and 5A, an electrical braking system isschematically illustrated and generally designated 200. In electricalbraking system 200, the braking unit is one or more resistors 202. Whenthe brakes are applied to the rotor hub assembly, the kinetic energy ofthe freely-rotating rotor hub assembly, supported by mast 206, isconverted into electrical energy by generator 204, which resistor 202then dissipates as heat into the atmosphere. The electric load providedby resistor 202 may be selectively engaged with generator 204 via switch207, which may be controlled by a pilot of the rotorcraft or fromelsewhere. Because the electrical energy is ultimately dissipated,electrical braking system 200 is a rheostatic braking system.

In some embodiments, resistor 202 may be one or more variable resistors.In such embodiments, the resistance provided by resistor 202 may beselected by the pilot or modulated by a computer system to adjust thebraking force applied to the rotor hub assembly. The variable resistormay also modulate the pilot's input to prevent over-braking. Forexample, if a pilot incorrectly applies a maximum braking force viainput controls in the cockpit, the variable resistor may apply aless-than-maximum resistance to generator 204 so that over-braking ofthe rotor hub assembly does not occur. In other embodiments, resistor202 may be a bank of multiple resistors applied in series or parallel togenerator 204. If applied in parallel, each of the resistors may have adifferent resistance value, and may be selected, individually or incombination, thereby allowing different electrical loads on generator204. In some embodiments, one or more vents, cooling fans or radiatorsmay be located adjacent resistor 202. The vents, cooling fans orradiators may help prevent the accumulation of heat at or near resistor202.

Referring specifically to FIG. 4, a schematic circuit diagram ofelectrical braking system 200 is shown in which armature 208 is inelectrical communication with resistor 202. Magnetic field 210 causesarmature 208 to reduce rotational speed when an electric load, such asresistor 202, is applied to the circuit that runs through armature 208.The flow of current in the circuit is shown by arrows 212, 214, 216. Insome embodiments, contactors 218, 220 are normally opened and contactors222, 224 are normally closed during braking operations. Contactors 222,224 may be opened or closed depending on whether resistor 202 is beingapplied as an electric load to generator 204.

Referring to FIG. 5B, a regenerative electrical braking system isschematically illustrated and generally designated 300. Instead of aresistor that dissipates electrical energy into heat, electrical brakingsystem 300 includes a rechargeable battery 302 in selective electricalcommunication with generator 304. Electrical energy produced bygenerator 304 is stored by rechargeable battery 302 for later use byelectrical components of the rotorcraft. In some applications,electrical braking system 300 may be installed on a rotorcraft thatalready has a rechargeable battery for use in other rotorcraftfunctions, thereby using existing componentry to minimize the weight,volume and cost of electrical braking system 300. In other embodiments,rechargeable battery 302 may instead be a capacitor or any otherelectrical storage device adapted to capture electrical energy producedby generator 304 for future use. The use of rechargeable battery 302enables electrical braking system 300 to convert the kinetic energy of afreely-rotating rotor hub assembly into a useful form of energy for useby the rotorcraft at any time. In a traditional disc-and-caliper brakingsystem, the kinetic energy of the freely-rotating rotor hub assembly iswasted. Therefore, electrical braking system 300 allows the rotorcraftto conserve energy by harnessing the kinetic energy of the rotor hubassembly during braking operations that would otherwise have beenwasted.

Referring to FIG. 5C, a regenerative electrical braking system isschematically illustrated and generally designated 400. The braking unitof electrical braking system 400 is a light source 402, such as a lightbulb or LED. The electrical energy produced by generator 404 duringbraking operations is used to power and illuminate light source 402. Inother embodiments, light source 402 may represent any electricalcomponent, including an electrical component that does not impederotorcraft shutdown or that dissipates energy. In other examples, theelectrical energy produced by generator 404 may be returned to a supplyline or power grid for the rotorcraft, such as a central powerdistribution system that powers the electrical components of therotorcraft. By powering the electrical components of the rotorcraft withthe kinetic energy of the freely-rotating rotor hub assembly, energy usefrom other power sources of the rotorcraft may be lessened or conserved.

Referring to FIG. 6, a hydraulic brake system is schematicallyillustrated and generally designated 500. Hydraulic brake system 500includes a hydraulic pump 502 that is mechanically coupled to mast 504,which in turn supports the rotor hub assembly. Hydraulic pump 502includes an input shaft 506 that rotates in response to rotation of therotor hub assembly. Hydraulic pump 502 also includes an input port 508and an output port 510. In the illustrated embodiment, rotation of inputshaft 506 causes hydraulic pump 502 to draw a fluid 512 from reservoir513 through a conduit 514 and input port 508, then to pump fluid 512 outthrough output port 510 to braking unit 516 via conduit 518. Brakingunit 516, which is in fluid communication with hydraulic pump 502, isadapted to selectively provide a braking force, in the form of hydraulicresistance or load, to hydraulic pump 502, thereby reducing a rotationalspeed of input shaft 506 and the rotor hub assembly. Hydraulic pump 502is operable to convert the kinetic energy of the rotor hub assembly intofluid energy, pressure and flow rate, which may then be dissipated,stored or used as necessary by braking unit 516.

In the illustrated embodiment, hydraulic pump 502 is mechanicallycoupled to the rotor hub assembly by gears 520, 522, 524, main rotorgear 526, as well as input shaft 506, shaft 528 and mast 504. Gears 520,522, 524, main rotor gear 526, input shaft 506, shaft 528 and mast 504are mechanically coupled between the rotor hub assembly and hydraulicpump 502 such that gears 520, 522, 524, main rotor gear 526, input shaft506, shaft 528 and mast 504 rotate in response to rotation of the rotorhub assembly. Thus, when hydraulic resistance is applied to hydraulicpump 502 by braking unit 516, the rotational speed of gears 520, 522,524, main rotor gear 526, input shaft 506, shaft 528, mast 504 and rotorhub assembly is reduced.

While hydraulic pump 502 is shown to be mechanically coupled to therotor hub assembly by gears 520, 522, 524, main rotor gear 526, inputshaft 506, shaft 528, mast 504, hydraulic pump 502 may be mechanicallycoupled to the rotor hub assembly by any number of gears, shafts, orother parts. Hydraulic pump 502 may be mechanically coupled to anyrotating portion of the drive system of the rotorcraft that ismechanically coupled to the rotor hub assembly. Also, hydraulic brakesystem 500 may be on the rotor side of a freewheeling unit such that therotor hub assembly is permitted to freely rotate input shaft 506 in theabsence of sufficient input from an engine, such as engine 24 in FIG.1A. In one example, shaft and gear 529 may be rotated, directly orindirectly, by the engine, which provides rotational energy to mainrotor gear 526 via gears 522, 524. In this example, the engine may beengaged or disengaged from shaft and gear 529 by a clutch. Afreewheeling unit may also be coupled to shaft and gear 529 so thatinsufficient input from the engine does not stall or prevent the freerotation of main rotor gear 526.

Hydraulic pump 502 may be any type of pump capable of moving fluid. Forexample, hydraulic pump 502 may be a gear pump, rotary vane pump, screwpump, bent axis pump, radial piston pump, peristaltic pump or flow pump,to name a few. Hydraulic brake system 500 may also include one or morecheck valves (not shown) to keep fluid 512 flowing in a desireddirection. For example, conduit 514 may include a check valve so thatfluid 512 is permitted to flow from reservoir 513 to hydraulic pump 502,but not in the opposite direction.

In some embodiments, hydraulic pump 502 may provide fluid energy toother hydraulically-powered components of the rotorcraft. In theseembodiments, hydraulic pump 502 is a pre-existing element of therotorcraft, eliminating the need to install additional componentry andreducing the weight, cost and complexity of the rotorcraft. In addition,multiple hydraulic pumps, such as hydraulic pump 502, may bemechanically coupled to the rotor hub assembly, and each hydraulic pumpmay support respective hydraulic brake systems, such as hydraulic brakesystem 500. By using multiple hydraulic brake systems 500, the brakingresistance provided to the rotor hub assembly may be fine-tuned based onthe particular operational needs of the particular rotorcraft.

Braking unit 516 is operable to apply a braking force to hydraulic pump502 in response to a braking signal input from the pilot of therotorcraft or from elsewhere. In some embodiments, fluid 512 may bediverted away from braking unit 516 until the braking unit 516 isfluidly engaged with hydraulic pump 502 during braking. Such a fluiddiversion may be accomplished by a hydraulic switch. In other examples,gear 520 may engage with gear 522 in response to the braking signalinput, thereby causing braking unit 516 to resist rotation of inputshaft 506 and slowing or preventing the rotation of the rotor hubassembly. Braking unit 516 may dissipate, store or use fluid energy, inthe form of pressure or flow rate.

Referring to FIG. 7A, a hydraulic braking system is schematicallyillustrated and generally designated 600. Hydraulic braking system 600includes hydraulic pump 602 that has input port 604 and output port 606.Hydraulic resistance to the rotation of input shaft 608 is provided byan adjustable orifice 610, which is in fluid communication with outputport 606. The fluid energy produced by hydraulic pump 602, which is inresponse to the rotation of the rotor hub assembly, is dissipated byadjustable orifice 610 by bleeding fluid pressure to reservoir 612 atselectively high flow rate. By adjusting the size of adjustable orifice610, fluid flow may be restricted and a selectable amount of fluidpressure may be allowed to build in conduit 614, thus providinghydraulic resistance to hydraulic pump 602. For example, during abraking operation, adjustable orifice 610 may be reduced to a small sizeto build the pressure of fluid 616 in conduit 614 to a level thatresists rotation of input shaft 608, and therefore the rotor hubassembly, by forcing hydraulic pump 602 to do more work. When thebraking operation has ceased, adjustable orifice 610 may be enlarged sothat fluid 616 may more freely flow into reservoir 612, which is influid communication with adjustable orifice 610. Adjustable orifice 610dissipates the fluid energy transmitted by hydraulic pump 602 in such away that hydraulic braking system 600 may be considered to be a dynamicbraking system.

By adjusting the size of adjustable orifice 610, the amount ofresistance provided by hydraulic pump 602 to the rotation of the rotorhub assembly may be modulated. For example, in the event that a pilotover-applies the brakes, adjustable orifice 610 may be contracted onlyslightly so that an over-application of resistance to the rotation ofthe rotor hub assembly does not occur. By actively braking therotorcraft in this manner, overall safety may be enhanced. In anotherembodiment, the size of adjustable orifice 610 may be automaticallycontrolled via a computer or manually via switches so that the correctamount of braking force may be applied to the rotor hub assembly inaccordance with the particular maneuver or braking operation takingplace. Adjustable orifice 610 may be any aperture capable oftransmitting fluid and that adjusts in response to input. In onenon-limiting example, adjustable orifice 610 includes a solenoid valve.The solenoid valve may be adjusted, via electronic input, to adjust thesize of the adjustable orifice 610.

Referring to FIG. 7B, a hydraulic braking system is schematicallyillustrated and generally designated 700. The braking unit of hydraulicbraking system 700 is a hydraulic accumulator 702 that is adapted tostore a pressurized fluid. When engaged, hydraulic pump 704 pumps fluid706 into hydraulic accumulator 702. Hydraulic accumulator 702 provides ahydraulic resistance, in the form of fluid pressure, to the rotation ofinput shaft 708, thereby providing resistance to the rotation of therotor hub assembly. In some embodiments, hydraulic accumulator 702 maybe kept in close proximity to hydraulic pump 704 and be adapted toachieve higher pressures not normally experienced by other components ofthe hydraulic subsystem of the rotorcraft. Hydraulic accumulator 702 andhydraulic pump 704 may be adapted to manage higher than normalpressures, while the rest of the hydraulic subsystem experiences normalhydraulic system pressures via a pressure regulator (not shown).

Fluid pressure may be stored in hydraulic accumulator 702 for later use.For example, the fluid pressure in hydraulic accumulator 702 may be usedto power one or more hydraulically-powered components of the rotorcraftat a later time. Such downstream components are signified in FIG. 7B byarrow 710. A non-limiting example of a component that may be powered bythe fluid pressure from hydraulic accumulator 702 is a hydraulicstarter. The various hydraulically-powered components that may bepowered by the hydraulic accumulator 702 are numerous.

Referring to FIG. 7C, a hydraulic braking system is schematicallyillustrated and generally designated 800. The braking unit of hydraulicbraking system 800 is a hydraulic blower 802. Hydraulic blower is ahydraulically-powered component that may utilize the fluid energyemanating from hydraulic pump 804 to perform a function (e.g., blowingair), while simultaneously providing hydraulic resistance to therotation of input shaft 806, thereby resisting the rotation of the rotorhub assembly. While FIG. 7C shows a hydraulic blower as thehydraulically-powered component that provides hydraulic resistance tohydraulic pump 804, any hydraulically-powered component may be used inhydraulic braking system 800, including those that do not adverselyaffect shutdown or braking of the rotorcraft.

The illustrative embodiments described above, including the hydraulicand electrical braking systems, may, in some implementations, notrequire the hardware of conventional rotorcraft brake systems, such asdisc-and-caliper braking systems. The illustrative embodiments may alsobe automatically controlled via computer, or manually via switches. Insome embodiments, automated braking may be possible in both theelectrical and hydraulic braking systems. In such automated brakingsystems, a pilot may engage the braking function while the braking unitdissipates rotor energy at a controlled rate while the pilot continueswith an operational checklist. The illustrative embodiments may alsoprovide protection for components of the rotorcraft by preventing thepilot from inadvertently over-applying the brakes.

In the example in which the illustrative embodiments use existingcomponentry of the rotorcraft, such as existing generators, alternatorsor hydraulic pumps, the illustrative embodiments may be designed to failin such a way that flight critical functions are not lost. Thus, failureof the electrical or hydraulic braking systems would not equate tofailure of either the electrical or hydraulic subsystems of therotorcraft, respectively. In some embodiments, both a hydraulic brakingsystem and an electrical braking system may be used on a singlerotorcraft. Either or both of the hydraulic or electrical brakingsystems may also be “blended” with traditional braking methods, such asdisc-and-caliper friction-based braking. In such blended brakingscenarios, the hydraulic or electrical braking system may, in someembodiments, be used to reduce the rotor hub assembly speed to apredetermined level, after which traditional braking methods take overto bring the rotor hub assembly to a complete stop. Other forms ofengagement and interaction between hydraulic, electrical and traditionalbraking systems may be utilized depending on the application.

The illustrative embodiments, including both the hydraulic andelectrical braking systems, provide a number of advantages, depending onthe embodiments utilized. For example, the illustrative embodiments mayreduce the number of parts on the rotorcraft. By reducing the number ofparts, labor may be saved by reducing part procurement and the number ofqualification/acceptance tests necessary for utilization of those parts.A lower number of parts may also be kept in inventory, and room may bemade on the rotorcraft for other components.

The illustrative embodiments may also reduce the weight of therotorcraft by eliminating an entire subsystem (e.g., disc-and-caliperbrakes). Such elimination of an entire subsystem may be made possible bythe utilization of existing components on the rotorcraft, such as thealternator and/or a hydraulic pump. The cost of the rotorcraft may alsobe reduced by reducing the installation time and number of components onthe rotorcraft. Maintenance and inspection of the eliminated parts is nolonger necessary, further reducing cost. Smart, or active, braking mayalso be achieved using the illustrative embodiments, thereby allowingautomated/computer-controlled braking to reduce pilot workload. At leasta portion of these advantages, as well as others, may be realized by theillustrative embodiments.

The foregoing description of embodiments of the disclosure has beenpresented for purposes of illustration and description. It is notintended to be exhaustive or to limit the disclosure to the precise formdisclosed, and modifications and variations are possible in light of theabove teachings or may be acquired from practice of the disclosure. Theembodiments were chosen and described in order to explain the principalsof the disclosure and its practical application to enable one skilled inthe art to utilize the disclosure in various embodiments and withvarious modifications as are suited to the particular use contemplated.Other substitutions, modifications, changes and omissions may be made inthe design, operating conditions and arrangement of the embodimentswithout departing from the scope of the present disclosure. Suchmodifications and combinations of the illustrative embodiments as wellas other embodiments will be apparent to persons skilled in the art uponreference to the description. It is, therefore, intended that theappended claims encompass any such modifications or embodiments.

What is claimed is:
 1. A braking system for a rotorcraft having a rotor hub assembly driven by an engine, the system comprising: a hydraulic rotary pump having an input shaft mechanically coupled to the rotor hub assembly such that the input shaft is rotatable in response to rotation of the rotor hub assembly, the hydraulic rotary pump selectably drivable by the engine; and a braking unit in fluid communication with the hydraulic rotary pump, the braking unit adapted to selectively provide a hydraulic resistance to rotation of the input shaft, thereby reducing a rotational speed of the rotor hub assembly.
 2. The braking system as recited in claim 1 wherein the braking unit further comprises an orifice operable to adjust the hydraulic resistance applied to the input shaft of the hydraulic rotary pump, the orifice adjustably contractable into an infinite number of positions.
 3. The braking system as recited in claim 2 further comprising a fluid reservoir in fluid communication with the orifice.
 4. The braking system as recited in claim 2 wherein the orifice further comprises a solenoid valve.
 5. The braking system as recited in claim 1 wherein the braking unit further comprises a hydraulic-powered component.
 6. The braking system as recited in claim 1 wherein the braking unit further comprises a hydraulic accumulator adapted to store a pressurized fluid usable to power a hydraulic-powered component of the rotorcraft.
 7. The braking system as recited in claim 1 wherein the hydraulic rotary pump is selected from the group consisting of a gear pump, a rotary vane pump, a screw pump, a bent axis pump, a radial piston pump, a peristaltic pump, a rotary positive displacement pump and a flow pump.
 8. The braking system as recited in claim 1 wherein the rotorcraft is operable in a storage mode, the braking unit engaged in the storage mode to prevent rotation of the rotor hub assembly.
 9. The braking system as recited in claim 1 wherein the rotorcraft is operable in a grounded mode, the engine disengaged from the rotor hub assembly in the grounded mode.
 10. The braking system as recited in claim 1 wherein the hydraulic rotary pump is in constant engagement with the rotor hub assembly via one or more gears during all operations of the rotorcraft.
 11. The braking system as recited in claim 1 wherein the braking unit further comprises a hydraulic accumulator adapted to store a pressurized fluid usable to power a hydraulic starter of the rotorcraft.
 12. The braking system as recited in claim 1 wherein the braking unit further comprises a hydraulic blower.
 13. The braking system as recited in claim 1 further comprising a disc-and-caliper braking subsystem.
 14. The braking system as recited in claim 13 wherein, in response to a braking input, the braking unit slows the rotor hub assembly to a predetermined level prior to the disc-and-caliper braking subsystem slowing the rotor hub assembly from the predetermined level to zero revolutions per minute.
 15. The braking system as recited in claim 1 wherein the engine further comprises a motor.
 16. A rotorcraft, comprising: a fuselage; an engine disposed in the fuselage; a rotor hub assembly protruding from the fuselage, the rotor hub assembly driven by the engine to rotate relative to the fuselage; a hydraulic rotary pump having an input shaft mechanically coupled to the rotor hub assembly such that the input shaft is rotatable in response to rotation of the rotor hub assembly, the hydraulic rotary pump selectably drivable by the engine; and a braking unit in fluid communication with the hydraulic rotary pump, the braking unit adapted to selectively provide a hydraulic resistance to rotation of the input shaft, thereby reducing a rotational speed of the rotor hub assembly.
 17. The rotorcraft as recited in claim 16 further comprising a gearbox containing a plurality of gears, the hydraulic rotary pump mechanically coupled to the rotor hub assembly via at least one of the plurality of gears.
 18. The rotorcraft as recited in claim 16 wherein the engine is operable to selectively provide rotational input to the rotor hub assembly; and wherein the rotor hub assembly is operable to freely rotate in response to mechanical disengagement between the engine and the rotor hub assembly.
 19. The rotorcraft as recited in claim 16 wherein the braking unit applies the hydraulic resistance in response to a braking signal input from a pilot of the rotorcraft. 